1. Field of the Invention
This invention relates to an electrical terminal comprising an inner contact body and an outer back-up spring, the terminal comprising contacts for making electrical connection between the back-up spring and the contact body to ensure good electrical connection between the inner contact body and a short circuit spring terminal making contact on an outer surface of the back-up spring.
2. Summary of the Prior Art
In the electrical industry it is common to find the use of terminals having an inner contact body and an outer back-up spring. The outer back-up spring is usually made of a metal such as stainless steel having good spring properties which are not altered by high mechanical solicitation such as vibration, or high temperatures, the outer back-up spring serving to increase the spring force of the inner contact body for increased electrical conductivity at the contact surfaces of mating terminals. Due to the back-up spring, the inner contact body can be manufactured from a good conducting material that also has good crimping properties for connection to conducting wires, these materials usually having poor spring properties. Such terminals are described in the following European patent application publications 0517076, 0517077, 0517139, which are included herein by way of reference. Terminals with outer back-up springs such as described above, can be used in many different applications, but find many applications in automobile connectors which are subject to harsh environmental conditions such as vibration, temperature and corrosive agents such as salt. Such terminals are also found in connectors for the detonation of airbags in the event of collision. Airbag connectors comprise short circuit spring terminals that electrically connect certain adjacent terminals thereof when the airbag connector is unmated (for maintenance or repair reasons for example), the short circuit spring terminal ensuring that the electrical potential difference between certain adjacent unmated terminals is zero to preclude unwanted detonation of the airbag. Good electrical contact between the short circuit spring terminal and the inner contact body of the adjacent terminals must therefore be guaranteed. Unfortunately, although there is contact between the outer back-up spring and the inner contact body, electrical contact therebetween is unreliable due to oxide layers forming between the contact surfaces of the inner contact body and outer back-up spring. The outer back-up spring material is chosen for it's main function, which is to support and increase the contact force of the inner contact body against a mating terminal, and also to provide retention means for locking the terminal in the cavity of connector housing, the electrical contact properties between the inner contact body and the outer back-up spring having been a second consideration. The inner contact body commonly is tin plated whereby the outer back-up spring is typically of stainless steel. In a corrosive environment, an oxide layer will form on the tin plating which will adversely affect electrical contact between the outer back-up spring and the inner contact body, the latter effect being aggravated by the electrolytic potential formed therebetween due to the different contact materials.
The outer back-up spring renders access to the inner contact body difficult for the short circuit spring which must therefore make contact with the outer back-up spring. The contact of the short circuit spring terminal is gold plated to preclude oxide layers forming thereon. The outer back-up spring, even though made from stainless steel, may still oxidize under a very corrosive environment such as the salt found in automobiles, once again accentuated by the differing contact materials.